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randomic

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Everything posted by randomic

  1. +1 for the Baader Hyperion Zoom, it's supposedly not parfocal when changing focal length but it's so close that I can't tell whether or not I need to refocus. I think rather than a barlow it might be better to grab a ~5mm eyepiece to get close to max useful magnification without needing extra glass. That said, a barlow can be used with imaging so you might find it useful to have.
  2. I notice in a lot of sun pictures there's no limb darkening. Is this due to a filter used or does increasing contrast in processing hide it? Beautiful pictures by the way, I'm looking forward to the increase in solar activity!
  3. The mirror should be in the position such that the in-focus image is formed 133.35mm behind the end of the OTA threads. Does that make sense? SCTs can form an in-focus image at a wide range of image plane distances but, with EdgeHD 800, the image plane at which the integrated flattener performs best is the one at 133.35mm Yeah there is some fine focus adjustment to compensate for things like the mirror shape changing due to temperature.
  4. Haha you're totally right, they do look a bit non-traditional! For me it looks extremely odd when I have the DSLR on the back, like I've got a 'silenced' camera lens or something 😂. With a dew shield on it looks a lot more "in proportion". I've not felt the weight of a dob but I believe they're a lot lighter than they look but I would still say better safe than sorry when it comes to your back! That's dedication but it's one hell of a piece of furniture! I'm sure it'll look great!
  5. I don't think they keep live stock updates on the website. I've found they respond pretty quickly after I shoot them an email 🙂
  6. Yeah I believe it's f/2 and f/5 respectively, I haven't looked in to the exact maths, maybe I'm closer than I thought!
  7. I've had a lot of luck recently with https://www.widescreen-centre.co.uk/ for stuff which has been out of stock everywhere else. Feedback for the retailer on this site hasn't been perfect but I've had absolutely no issues with them so far. They've always been super helpful and quick to respond to any questions/stock-checks.
  8. Yeah you're absolutely right, and if you look at any of Celestron's marketing material you'll see that all the focal lengths are quoted at 10x the aperture. Presumably because it's a nice round number to say it's f/10. In the whitepaper, however, it seems that they've actually done some measurements; the EdgeHD 800 for instance is listed at f/10.456 Fundamentally, as you say, the roundness of stars is all that matters!
  9. It's a good shout! I think one of the original Celestron documents had the distance indicated incorrectly in the diagram. I am indeed measuring from the red line. Maybe I just need to double check everything. I've got a ZWO camera on its way which should allow me to measure all the way to 6.5mm from the chip, it could be that my DSLR + T-ring is a ways off of 55mm.
  10. An alt-az goto scope like the Celestron Nexstar series might be that midpoint. They're quick to set up, you can get an accessory which allows it to align itself (although it's not difficult to do it yourself) and it's relatively easy to take pictures through the eyepiece using even just a smartphone. The main limitation of alt-az is exposure length, due to the Earth's axis of rotation not matching either of the scope's axes the field rotates in the eyepiece over time. This can be solved to some extent using a wedge.
  11. I've got a 462mc on the way. Very excited after seeing this, those views in IR are stunning, so sharp!
  12. I think the bigness of dobs mainly comes into play when you're not using it. If you have a (relatively) dust free place you can store it then you'll have no worries. It might be a little faff to move outside on a clear night but once you've moved it.. that's it, it's ready for observing! There's a beautiful simplicity. When setting up my kit I have to make around 8 trips back and forth with a bunch of awkward to carry stuff and then go through all the various rituals to get everything balanced and aligned. Sure, it's necessary for imaging but there are no real shortcuts for me if I just fancy having a quick look at the moon before the clouds roll in. It can often take me around an hour to start actually collecting data (although I am getting better at it). Edit: If you do go for a dob then make sure (if you haven't already) to get a copy of Turn Left at Orion, it's an absolutely wonderful book for exploring the sky without the need for computer control and there is great reward in managing to find objects on your own.
  13. You mention being put off by reflectors due to their bulk. I presume you are referring to Newtonian (Dobsonians) designs? These are often recommended because they give you the most aperture/£ which is a great thing for visual. You are right that they take up a lot of space though. Have you considered a Schmidt–Cassegrain design? They can be a bit pricey but they put a lot of aperture and focal length (which is great for observing planets) into a compact package. Something like a Celestron NexStar 4SE or 6SE perhaps? 80mm refractors are a fantastic platform for imaging large nebulae but I can't help but feel you'd be disappointed with the 200x max (theoretical) magnification for visual planetary observing. P.S. That planisphere is amazing!
  14. Celestron's EdgeHD product line features an integrated field flattener. As with all flatteners, these produce optimal results when the imaging plane is a specific distance from the flattener. In the EdgeHD whitepaper Celestron describe the optimal backfocus of 133.35mm (5.25") for the 8" model, and 146.05 (5.75") for the 9.25", 11" and 14" models. They suggest that the image plane should be placed within 0.5mm of this distance. When putting together an imaging train it can be quite hard to determine the actual backfocus. You could add together all the optical lengths quoted by manufacturers, you could get calipers and actually measure each part or even try to measure the entire thing (although it can be quite hard to figure out where to measure from. At some point, you have to trust some manufacturer spec (unless you fancy risking your sensor). Once all this is done you might, however, find that things vary ever so slightly; everything from the tightness of threads to the T-ring not quite giving exactly 55mm. How do you work out if you've done it all correctly? In a table in the whitepaper (page 13), focal lengths are given for each OTA (for example 2125mm for the 8" model). Hypothetically then, it should be possible to measure whether or not you're at optimal backfocus by plate solving for your image scale. In the same table, an image scale is given for a sensor with pixel size 6.4 micron but you can use a calculator (such at the astronomy.tools one) to work out the expected image scale for your particular sensor. This does require that your image is as close to perfect focus as possible. Putting all this into practice. I used my calipers to try to get the image train as close to 133.35mm as I could and then plate solved some resulting data taken with a DSLR with 5 micron pixels. From my calculations, if I'm in focus at the correct spacing, I should have an image scale of 0.485"/pixel. However, my astrometry.net solves gave an image scale of 0.495"/pixel. Working backwards, this indicates that I was at a focal length of 2083mm, quite a way inside 2125mm. Although I can't find a reference I've read that, for an SCT, the focal length changes by approximately 3mm for each 1mm of backfocus, this implies that my sensor is 14mm too close! Now, I'm no expert with calipers but I feel like I couldn't have been more than a few mm out, and if anything I thought I was too far. I suppose I could have been a bit out of focus but surely not ~10mm. Is there a mistake in my logic of aiming for 2125mm focal length?
  15. Swinton, I'm afraid, a little further away 😁; suburb near Manchester
  16. Hello everyone, I've always wanted my own telescope ever since studying physics. ~10 years on, and thanks in some part to not being able to go out and spend money right now, I finally have the disposable income to get stuck right in. Bought an HEQ5 Pro (felt like the last one in the entire country at the time) and an EdgeHD 800. After spending the first few clear nights getting to grips with the kit visually (the Baader Hyperion zoom eyepiece is wonderful) and integrating an old raspberry pi for remote control I cobbled together all the various adapters and attached a Nikon D3100. Had a great night collecting data from M13 and fiddled around in DSS/StarTools to get a result that I'm pretty happy with. I also captured around 45 mins of data of M33 however it was all but ruined by dew 🙃 I've also got an ASI 462mc coming, hopefully in time for Mars' opposition, so looking forward to getting some shots of that in infrared. Hope everyone's well and safe and clear skies! Jay Target: M13 (The great cluster in Hercules) Data: 49x 60s, Sky brightness around mag 18.8 (probably a bit worse due to the full moon) Mount: Skywatcher HEQ5 Pro (unmodded, unguided) OTA: Celestron EdgeHD 800 Sensor: Nikon D3100 (1600 ISO) astrometry.net upload: https://nova.astrometry.net/user_images/4042276 P.S. Can you spot IC 4617?
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